Loonrat
A great thought provoking post. Our backgrounds and display experience are somewhat different but the lessons and philosophies inevitably will be the same. I started display flying in 1984 and am still displaying now, with my experience covering both CAA and UK Military regulation, and types covering swept wing fast jets and single piston (cat B and C) types. A few thoughts to continue the debate:
Barrel Rolls To fly barrel rolls in a display in the way that the UK Military teaches barrel rolls would indeed be dangerous. However, there are many ways to fly them and some techniques can be flown in a display consistently and safely. The military teach to achieve a very high nose up pitch attitude at the end of the first quarter when at 90 degrees of bank, and for a symmetrical manoeuvre pitch attitude on the way up will equal pitch attitude on the way down and, therefore, height loss in the second half may be excessive. Also, I believe that some do not stress the importance of achieving wings level inverted at the apex and absolutely no later than when the nose passes the horizon. However, watch how the Red Arrows, for example, fly a barrel roll. At the start they will remain wings level until about 35 degrees nose up and then will start to roll and simultaneously reduce the nose up pitch rate, achieving wings level inverted at the apex then continuing with a constant rate of roll and relatively low pitch rate. As a singleton you can start this manoeuvre from a level turn in the opposite direction to the roll then commence the roll from the turn whilst maintaining the nose up pitch rate such that you achieve the same wings level attitude at around 30 - 35 degrees nose up. These most certainly are barrel rolls and are, in my opinion and experience, safe to fly in a display. But to return to the original post, I too have had friends killed in barrel rolls during displays, inevitably as a result of an excessively high nose up pitch attitude during the first half and failing to achieve wings level by the apex.
Minimums It is worth adding detail regarding which minima you can fly to safely and for which you should ideally always have a margin. Minimum heights, for flypasts or for aerobatics, are approved for a given pilot based on the category or type of aeroplane and the pilot's experience and skill. Therefore, if a minima has been awarded then I see no reason why a pilot should not fly to it if and when appropriate. For a deep crowd it perhaps should not be used because the spectators at the rear may not be able to see the aeroplane. However, for a thin crowd line flying at the minima will quite possibly give the best view of the aircraft, especially for photographers who will then have a background. BUT, the minima that should have the extra margins added whenever possible relate to the energy of the aircraft, specifically the minimum entry speed for a vertical manoeuvre and the minimum height required for successful completion of a pull through/downward half of a loop. In those cases, in my opinion the minima should only be used if there is a real 'safety of flight' reason for doing so.
Risk Assessments These are fine for the risks that have been envisaged and anticipated. However, there will always be risks out there that you have not thought about and are, perhaps, novel. These may well be associated with manoeuvres and conditions that are permitted within the regulatory approvals so mitigating them is down to you! Risk assessments will not save you from these but sound judgement based on experience, common sense and a sense of self preservation might. Be alert, think everything through and never believe that if a risk assessment is signed off that you are safe.